1. Field of the Invention
The present invention relates to a sheet processing apparatus and a sheet processing method which stack sheets which have been conveyed.
2. Description of the Related Art
A conventional sheet processing apparatus conveys sheet by sheet sheets discharged from an image forming apparatus to an intermediate processing tray to stack the sheets on the same, and carries out predetermined post processing such as stapling set in advance on an operating screen of the image forming apparatus, on a bundle of sheets stacked on the intermediate processing tray. After discharging the post processed bundle of sheets from the intermediate processing tray, the sheet processing apparatus waits for the next sheets conveyed from the image forming apparatus.
A sheet processing apparatus has been disclosed by Japanese Laid-Open Patent Publication (Kokai) No. 2001-97631, which is provided with a sheet buffer mechanism that operates to keep constant intervals between sheets discharged from an image forming apparatus to thereby secure a proper time period for carrying out post processing and sheet bundle discharge processing.
However, the conventional sheet processing apparatus have the following problem, which has been desired to be solved. That is, to secure the time period for processing a bundle of sheets processed on the intermediate processing tray, it is necessary to keep sheets discharged from the image forming apparatus in a waiting position until the processing of the preceding bundle of sheets is completed, leading to degraded processing efficiency.
To provide the sheet buffer mechanism in the sheet processing apparatus, a space for provision of the mechanism is required, leading to an increased size of the apparatus and increased costs. Therefore, the sheet processing apparatus with the sheet buffer mechanism is not suitable for use as a sheet processing apparatus attached to an image forming apparatus which has a relatively low processing speed.